Thursday, July 21, 2011

Cat litter to become an edible product?

Sepiolite is a lightweight porous mineral used in cat litter and other applications. The extraordinary properties of this clay make it a highly sought after mineral, despite its scarcity in Earth's crust: only a few mines worldwide extract it, several of them clustered near Madrid in Spain, the world's biggest exporter of this material.

Sepiolite has been known since Roman times when it was used to filter and purify wine, but our understanding at the atomic scale of how these tiny crystals absorb enormous amounts of liquid has remained elusive until now. A team of scientists from Spain and France has obtained for the first time single-crystal X-ray diffraction images of sepiolite, opening the path to industrial synthesis and further improvement of its properties. The results will be published in the October 2011 issue of the journal American Mineralogist.

The team included scientists from the Universities of Madrid and Salamanca in Spain, of the Institut Laue-Langevin (ILL), the European Synchrotron Radiation Facility (ESRF), and the Spanish CRG Beamline at the ESRF (SpLine), all in Grenoble (France).

No other mineral is known to absorb more water or other liquids as efficiently as sepiolites. The reasons are its structural nanoporosity due to tunnels in the crystals, and the fact that the elongated, needle-shaped sepiolite crystals pack very loosely into a lightweight porous material. The surface area ranges between 75 and 400 m2/g, meaning that 20g of mineral have an internal surface equivalent to that of a football court. This is why sepiolite can absorb 2.5 times its weight in water. The tunnels in the crystal structure along with the empty space between the needles form a capillary network through which liquids can easily flow deep inside the bulk where the molecules attach to the surface of the crystals.

The tiny size of these crystals -- they measure a few micrometres in length and as little as some dozen atoms across -- has been the main obstacle to their being studied with single-crystal diffraction techniques. For this experiment, the scientists collected samples of sepiolite fibres from twenty different deposits around the world. These fibres, each made of many crystals, were first imaged with electron-microscopy and then studied using X-ray powder diffraction.

However, the most accurate technique to resolve the three-dimensional structure of a crystal is single-crystal diffraction with either X-rays or electrons as probe. "To study very small crystals, the ESRF uses an X-ray beam with just 2 by 5 micrometres cross section. In the end, we collected X-ray diffraction data for two fibres," says Manuel Sanchez del Rio from the ESRF, "but the data were not easy to interpret, and needed extensive computer simulations to confirm and refine the information gathered by electron diffraction experiments done in parallel at the University Complutense of Madrid."

The wide variety of sepiolites studied is now enabling the team to correlate between the physical and chemical properties of a given type with its atomic structure. "Today, no synthetic clay surpasses natural sepiolite. This is about to change as our understanding of their atomic structure will guide the synthesis of sepiolites from other, more abundant clay minerals and the design of completely new materials for use in catalysis and batteries," says Mercedes Suárez from the University of Salamanca.

"The future of sepiolites in the household is outside the litterbox. Already today, they absorb liquid spillages and odours and stabilise aqueous products like paints, resins and inks. In synthetic form, they could bind food products and stabilise drugs, extending their shelf life and making sepiolite an edible product," concludes Manuel Sanchez del Rio.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by European Synchrotron Radiation Facility.

Journal Reference:

Manuel Sanchez del Rio, Emilia Garcia-Romero, Mercedes Suarez, Ivan da Silva, Luis Fuentes Montero, and Gema Martinez-Criado. Variability in sepiolite: Diffraction studies. American Mineralogist, 2011 DOI: 10.2138/am.2011.3761

Chemistry: Separation a thousand-fold faster may lead to new composite materials

 Numerous industrial processes make use of blends. Researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences have studied how the external electric field affects the rate of component separation in blends composed of polymers and liquid crystals and those composed of various types of polymers. The observations gathered open interesting opportunities, e.g., for the development of new composite materials.

Inhomogeneous blends of polymers with other polymers or liquid crystals are widely used in industrial applications -- in LCD displays, gas-flow sensors, optical memories and other devices. Researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw analysed the behaviour of such blends in alternating external electric field. „We managed to determine precisely the conditions permitting even a thousand-fold acceleration of component separation process in the blends under study," says Prof. Robert Hołyst.

With time, many blends separate spontaneously into their components, usually at a very low rate. It has been known since long that the separation can be accelerated when an inhomogeneous liquid is placed in an external alternating electric field with adequately tuned frequency. It is generally accepted that the acceleration of separation is due to ions -- natural constituents of such mixtures.

The researchers from the Institute of Physical Chemistry of the PAS studied blends of a polymer with another polymer or liquid crystal. In the presence of an alternating electric field with the strength of several million volts per meter the ions of the component with higher conductivity start to move freely towards the electrode with the opposite charge. Having reached the phase interface with a non-conductive material on the other side they are strongly hampered. „Under these conditions, an additional force appears at the interface. With electric field alternating at appropriate frequency the ions start to yank the interface. Due to the yanking, the droplets of a component merge with each other significantly more efficiently than in the normal case, thus leading to a faster separation of both phases," says Natalia Ziębacz, a PhD student at the IPC PAS.

The separation efficiency of studied blends into their components is strongly dependent on the frequency of the applied electric field. Optical measurements carried out at the IPC PAS have shown that under optimal conditions, at frequencies up to the kilohertz range, the separation takes place even thousand-fold faster. Too low or too high frequencies of the electric field do not result in significant movements of ions and the separation occurs at a regular, low rate. The physical mechanism of the phenomenon suggests that similar effect can be expected in all blends contaminated with ions and containing components with different charge conductivities.

Controlling the rate of separation process over so long time range, extending over three orders of magnitude, opens the way to interesting applications. The separation process can be carried out very quickly, and then virtually stopped at a precisely selected stage. The structure of the blend so obtained can be then fixed, for instance by changing the temperature. Thus, the method to control separations of blends of polymers and liquid crystals using electric field turned out to be an excellent tool for the development of new materials. A patent application for the method has been filed.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by Institute of Physical Chemistry of the Polish Academy of Sciences, via AlphaGalileo.

Journal Reference:

Natalia Zie?bacz, Stefan A. Wieczorek, Tomasz Szymborski, Piotr Garstecki, Robert Hołyst. Thousand-Fold Acceleration of Phase Decomposition in Polymer/Liquid Crystal Blends. ChemPhysChem, 2009; 10 (15): 2620 DOI: 10.1002/cphc.200900505

Conducting energy on a nano scale: Are 'doped' nanocrystals the future of technology?

Modern electronics as we know them, from televisions to computers, depend on conducting materials that can control electronic properties. As technology shrinks down to pocket sized communications devices and microchips that can fit on the head of a pin, nano-sized conducting materials are in big demand.

Now, Prof. Eran Rabani of Tel Aviv University's School of Chemistry at the Raymond and Beverly Sackler Faculty of Exact Sciences, in collaboration with Profs. Uri Banin and Oded Millo at the Hebrew University, has been able to demonstrate how semiconductor nanocrystals can be doped in order to change their electronic properties and be used as conductors. This opens a world of possibilities, says Prof. Rabani, in terms of applications of small electronic and electro-optical devices, such as diodes and photodiodes, electric components used in cellular phones, digital cameras, and solar panels.

Solar panels are typically made from a pn junction. When they absorb light, the junction separates the negatively charged electrons and the positively charged holes, producing an electrical current, explains Prof. Rabani. "With this new method for doping nanocrystals to make them both p and n type, we hope that solar panels can be made not only more efficient, but cheaper as well," he says. This research has been published recently in the journal Science.

Crystal-clear progress

According to Prof. Rabani, the quest to electrically dope nanocrystals has been an uphill battle. The crystals themselves have the capacity to self-purify, which means that they cleanse themselves of dopants. Also, he adds, some of the synthetic methods for doping were problematic on the nano-scale -- the crystals were unable to withstand doping techniques applicable to bulk semiconductors.

The key, explains Prof. Rabani, was to find a method for doping the nanocrystals without "bleaching" their optical properties -- and therefore nullifying their absorption capabilities. If you can dope nanocrystals in this way, he says, it opens the door to many practical applications based on nanocrystalline materials. "Whatever you can do with nanocrystals, you can do with doped nanocrystals -- and more by controlling their electronic properties."

These challenges were circumvented with the use of room temperature diffusion controlled reactions. The crystals were bathed in a solution that included the dopants, where slow diffusion allowed for impurities to find their way into the nanocrystal.

The researchers used a scanning tunneling microscope (STM), a device that images surfaces at an atomic level, in order to determine the success of their doping procedure. These measurements indicated how the Fermi energy of the nanocrystals changed upon doping, a key feature in controlling the electronic properties of electronic devices. The results, notes Prof. Rabani, indicate that the nanocrystals have been doped with both n-type dopants, indicating the presence of excess electrons in the nanocrystals, and p-type, which contribute positively charged holes to the semiconductors. This will allow for their use in electronics that require a pn junction, such as solar panels, light emitting diodes, and more.

Broadening the nanocrystal spectrum

Not only did Prof. Rabani and his fellow researchers succeed in doping nanocrystals without bleaching their optical properties, but they also were able to control the optical properties, namely, the color range that the nanocrystals produce. Once doped, the nanocrystal particles could change in color, becoming more red or blue. Prof. Rabani and his colleagues were able to develop a theory to explain these observations.

Prof. Rabani says that this technology can go a long way. Doping semiconductors, he explains, has been essential for the development of technology. "Parallel to this, we also know we want to make electrical components very small. A big portion of future electronics or optics is going to be based on doping nanoparticles."

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by American Friends of Tel Aviv University.

Journal Reference:

D. Mocatta, G. Cohen, J. Schattner, O. Millo, E. Rabani, U. Banin. Heavily Doped Semiconductor Nanocrystal Quantum Dots. Science, 2011; 332 (6025): 77 DOI: 10.1126/science.1196321

Innovative system for producing carpets

In Europe 700 million square metres of carpets are produced each year, and in the United States the volume is ten times higher.

The work has been carried out for the Netherlands companies Bond Textile Research, Best Wool Carpets and James, which own the four patents on which this new biological technology is based.

The so-called "cradle-to-cradle" model has been central to the work done by the team led by Tzanko Tzanov, a researcher with the Molecular and Industrial Biotechnology Group at the Universitat Politecnica de Catalunya. BarcelonaTech's Terrassa Campus. The outcome is an enzyme-based biological technology that paves the way for three Netherlands companies to manufacture carpets that are much lighter, sustainable, biodegradable, and 100% recyclable. At the end of their useful life, the carpets can be used as fertiliser or substrate for growing plants. The system saves a great deal of energy, completely closes the biological cycle for wool, and significantly reduces the final cost of carpet products.

For the last year, Tzanko Tzanov, one of the coordinators of the Molecular and Industrial Biotechnology Group at the UPC's Terrassa Campus, has been working in collaboration with researchers at the University of Graz (Austria) on the project, which is known as Erutan ("nature" backwards). The "back to nature" concept is at the heart of the research project commissioned by the Netherlands companies Bond Textile Research, Best Wool Carpet and James, who asked the team to come up with a technology for manufacturing wool carpets that would close the biological cycle for wool and avoid the use of latex.

Doing without latex

In line with the cradle-to-cradle philosophy, Tzanov's team focused on creating a product that can be returned to nature at the end of its useful life in the form of organic material for growing plant products. To achieve this goal they had to eliminate latex -- a material that is both heavy and expensive -- from the manufacturing process for wool carpets. Conventional manufacturing of carpets includes a system for binding the material using a layer of latex that impregnates the backing to which fibres are attached. This layer of latex (a very costly material) accounts for 70% of a carpet's weight and must be applied by means of high-temperature vulcanisation. Normally when a carpet reaches the end of its useful life it is destroyed by incineration, a process that generates greenhouse gases. Only 20% of the product is recycled.

Enzymes generate powerful adhesive

The research team focused on harnessing enzymes in the production process. The innovative system they developed starts with a thorough check of the wool used, which comes from New Zealand sheep that graze on organic pastures free of pesticides and heavy metals. When the wool reaches the production facility, it undergoes an enzyme-based pre-treatment process that cleans the material and removes all the impurities found in raw wool.

After the wool is spun and cross-linked to the carpet base, the backing is impregnated with a paste made ??of natural phenolic compounds and oxidative enzymes that polymerise the paste. This process produces a powerful adhesive that creates the platform to which the fibres are attached. The wool is bound in a more compact, durable way, yielding a product that beats durability standards for carpets made using conventional systems by two points.

Energy savings

The enzymatic treatment takes 30 minutes and comprises two stages. In the first, the carpet must be kept at a temperature of 45°C for 15 minutes, and in the second, a temperature of 95°C is maintained for an additional 15 minutes. The process uses 50% less energy than the conventional treatment, which requires vulcanisation at 100°C to treat the latex.

From carpet to substrate for growing mushrooms

A wool carpet manufactured using this innovative system is a completely natural and biodegradable product. At the end of its useful life the entire product can be shredded and turned into organic material, which can then be used, for example, as fertiliser for growing plant products. In fact, the company BVB Substrates is currently testing this organic material as a substrate for growing plants.

Carpet production is a large-scale activity. In Europe 700 million square metres of carpeting is produced each year, 55 million square metres of which is with latex backing. In the United States, the production volume is ten times higher. Mohawk Industries, the leading US carpet manufacturer, has expressed an interest in the new production system.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Universitat Politecnica de Catalunya (UPC), via AlphaGalileo.